Long Island Nice Tea
A Top-Five Hottest Year Despite Relief from Major Storm Systems
The Importance of the Long Island Sound Region
For analyses like these that characterize environmental conditions for a particular area—in this case, the Long Island Sound—it is important to be clear about the spatial extent that defines the region of study; different domain boundaries could produce different results. The spatial area we use to define the “Long Island Sound” is displayed in Figure 1, and has remained consistent throughout our seasonal and annual warming updates.
Highlights from Another Remarkably Warm Year
Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Long Island Sound. To keep you informed, we share seasonal and annual updates about conditions in the Long Island Sound.
With an annual average sea surface temperature (SST) of 56.48°F — more than 1.99°F above normal — the Long Island Sound experienced its 5th warmest year on record in 2023. This year fell short of the previous warmest year on record — 2021 — 1.12°F, but was record-breaking in a number of regards.
The first four months this year average monthly SST was within the top 3 warmest among all years on record. With February, March, and April all the warmest on record.
The most extreme temperatures in 2023 occurred in February and March, each setting new records for highest monthly average SST in the Long Island Sound.
The “coolest” monthly average temperature anomalies for 2023 occurred during September, November, and December. Each of last five months this year had SSTs below the top ten warmest.
SSTs in 2023 were consistent with the long-term trend of increasingly warm conditions driven primarily by anthropogenic climate change.
2023 Sea Surface Temperature in the Long Island Sound
Comparing Annual SST to Historical Conditions
When we compare the annual average SST in the Long Island Sound for 2023 (56.48°F) to other years, we can see it narrowly beat out 2012 as the second warmest year on record. When we look at the deviation from the long-term average SST (i.e., the annual SST anomaly), the last decade stands out for its exceptional warmth (Figure 3). 2023 extends a pattern that began in 2010 of sustained above-average temperatures. With the exception of 2019 (ranked 13th), every one of the last ten years remains in the top 10 warmest years on record.
Annual Ranks
Monthly Rankings
?(caption)
| Table 1. Monthly Average Sea Surface Temperatures - 2023 | ||||
| Month | Rank (1982-2023) | Observed Temperature | Climatological Average | Temperature Anomaly |
|---|---|---|---|---|
January |
10 |
41.1°F (5.1°C) |
39.8°F (4.3°C) |
1.4°F (0.8°C) |
February |
3 |
40.2°F (4.5°C) |
36.5°F (2.5°C) |
3.7°F (2.0°C) |
March |
3 |
41.1°F (5.1°C) |
38.0°F (3.4°C) |
3.1°F (1.7°C) |
April |
3 |
47.3°F (8.5°C) |
44.2°F (6.8°C) |
3.1°F (1.7°C) |
May |
4 |
56.3°F (13.5°C) |
53.2°F (11.8°C) |
3.2°F (1.8°C) |
June |
13 |
63.9°F (17.7°C) |
62.9°F (17.2°C) |
1.0°F (0.6°C) |
July |
2 |
74.0°F (23.3°C) |
70.3°F (21.3°C) |
3.7°F (2.0°C) |
August |
13 |
73.1°F (22.8°C) |
72.3°F (22.4°C) |
0.8°F (0.4°C) |
September |
7 |
72.0°F (22.2°C) |
70.0°F (21.1°C) |
1.9°F (1.1°C) |
October |
12 |
64.5°F (18.0°C) |
63.8°F (17.6°C) |
0.7°F (0.4°C) |
November |
9 |
55.8°F (13.2°C) |
55.0°F (12.8°C) |
0.8°F (0.5°C) |
December |
14 |
47.2°F (8.5°C) |
46.6°F (8.1°C) |
0.6°F (0.3°C) |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | ||||
| Climatological Reference Period: 1991-2020. | ||||
Annual Trends
Since the early 1980s, the rate of warming in the Long Island Sound 0.91°F / Decade has been more than triple that of the world’s oceans (0.29°F / Decade Figure 4). The precise causes of the pronounced jump in annual average SSTs in the region from 2009 to 2012 remains an area of active research, but the sustained warm conditions suggest a regime shift in the influence of major ocean currents (i.e., Gulf Stream vs Labrador Current) in the Long Island Sound. While a long-term increase in SSTs is expected as a result of human-caused climate change, we also expect each year to be influenced by large-scale patterns of natural variability, particularly on sub-global (i.e., regional) scales. SST conditions in the Long Island Sound for 2023 retain the region’s distinction as being one of the fastest warming ocean regions on the planet; including the 2023 data shows that the Long Island Sound is warming faster than 97% of the world’s ocean surface.
Quarterly Trends
Zooming in to sub-annual timescales reveals some interesting patterns: the observed rate of warming in the Long Island Sound varies throughout the year. Comparisons across the four quarters of the year (Figure 5) reveal that the Long Island Sound is warming fastest during July-September (~4x the global ocean average)—almost twice the rate seen during January-June (~3x the global ocean average).
Daily Sea Surface Temperatures
The annual cycle of SST in the Long Island Sound exhibits a pattern common to regions in the Northern Hemisphere, with the lowest temperatures observed in March and the highest values observed in August (Figure 6). Daily SST anomalies in 2023 never fell below +-1.73 °F compared to the long-term (1991-2020) average and reached as high as high as 5 °F above the long-term average.
The largest temperature anomalies were observed during November, which also turned out to be the warmest November on record (as highlighted in our Fall 2022 update). Figure 6 also illustrates that, in 2023, 353 days experienced SST anomalies that exceeded the threshold for being considered marine heatwaves, or MHW (more on MHWs below, including Figure 7)
MHW Temps
A marine heatwave (MHW) is defined as a period when there are five or more consecutive days when the observed SST is greater than the 90th percentile of the long-term average for that day. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event. Figure 6 illustrates that the Long Island Sound met the criteria for experiencing a MHW for 55 days in 2023 (or 97% of the year). Superimposing MHW status (black line) over the full timeseries of daily SST anomalies (blue/white/red shading) (Figure 6) reveals that the frequency, duration, and intensity of MHWs has increased in the past decade.
MHW Anomalies
MHW Heatmap
In a world without human-caused climate change, we would expect, positive (warm) and negative (cool) SST anomalies to more or less balance out over the span of several years, as various patterns of natural climate variability alternate having a dominant influence on Earth’s climate (e.g., La Niña vs El Niño). What is being observed in the Long Island Sound (and elsewhere around the world), however, is a loss of that balance: larger fractions of recent years are experiencing above average temperatures and cold spells are becoming vanishingly rare.
Record Temp Bars
Daily SST values in 2023 were some of the highest ever recorded in the Long Island Sound. Record high SSTs were set for more than half of all days during the months of February, March, & April. February saw the most new records, with 86% of days setting new daily record highs.
SST Map
In addition to the sub-annual (or temporal) variation, there can also be significant spatial variability in annually-averaged SST patterns. The Long Island Sound illustrated this fact, with the region southeast of Georges Bank exhibiting the highest annual average SST anomalies (Figure 9). This area is more susceptible than other areas in the region of study to large-scale variability in major oceanic currents, such as the relative influence of the Gulf Stream versus the Labrador Current.
Quarterly Map
Looking at these spatial patterns across the annual quarters of 2023 (Figure 10) shows not only the large spatial variability in SST conditions, but also how that spatial variability can, itself, vary significantly over the course of the year. While the open ocean beyond Georges Bank exhibits significant spatial and temporal variability, Figure 10 also illustrates that the Long Island Sound experiences more consistent SST conditions spatially and temporally (i.e., the entire region is anomalously warm throughout the year and the warmest areas tend to be those that are most heavily influenced by inflow from the Northeast Channel—the deep valley south of Nova Scotia and just off the northeast tip of Georges Bank).
A Note on Data Sources
The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.
- NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.